An interference detection strategy for Apertif based on AOFlagger 3

DOI: 
10.1051/0004-6361/202245022
Publication date: 
15/02/2023
Main author: 
Offringa, A. R.
IAA authors: 
Hess, K. M.
Authors: 
Offringa, A. R.;Adebahr, B.;Kutkin, A.;Adams, E. A. K.;Oosterloo, T. A.;van der Hulst, J. M.;Dénes, H.;Bassa, C. G.;Lucero, D. L.;Blok, W. J. G.;Hess, K. M.;van Leeuwen, J.;Loose, G. M.;Maan, Y.;Oostrum, L. C.;Orrú, E.;Vohl, D.;Ziemke, J.
Journal: 
Astronomy and Astrophysics
Publication type: 
Article
Volume: 
670
Pages: 
A166
Abstract: 
Context. Apertif is a multi-beam receiver system for the Westerbork Synthesis Radio Telescope that operates at 1.1-1.5 GHz, which overlaps with various radio services, resulting in contamination of astronomical signals with radio-frequency interference (RFI). <BR /> Aims: We analyse approaches to mitigate Apertif interference and design an automated detection procedure for its imaging mode. Using this approach, we present long-term RFI detection results of over 300 Apertif observations. <BR /> Methods: Our approach is based on the AOFlagger detection approach. We introduce several new features, including ways to deal with ranges of invalid data (e.g. caused by shadowing) in both the SumThreshold and scale-invariant rank operator steps; pre-calibration bandpass calibration; auto-correlation flagging; and HI flagging avoidance. These methods have been implemented in a new framework that uses the Lua language for scripting, which is new in AOFlagger version 3. <BR /> Results: Our approach removes RFI fully automatically, and it is robust and effective enough for further calibration and (continuum) imaging of these data. The analysis of 304 observations shows an average of 11.1% of lost data due to RFI with a large spread. We observe 14.6% RFI in auto-correlations. Computationally, AOFlagger achieves a throughput of 370 MB/s on a single computing node. Compared to published machine learning results, the method is one to two orders of magnitude faster.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2023A&A...670A.166O/abstract
ADS Bibcode: 
2023A&A...670A.166O
Keywords: 
instrumentation: interferometers;methods: observational;techniques: interferometric;surveys;radio continuum: general;Astrophysics - Instrumentation and Methods for Astrophysics